1. Field of the Invention
The present invention relates to a fluorine-containing copolymer which imparts excellent oil repellency, stain-proofing properties and soil releasability to articles to be treated such as textiles, and is excellent in washing-durability.
2. Background Art
As a stain-proofing agent which imparts water- and oil-repellency to fiber woven fabrics and the like, and also enables easy removal of stains adhered on fibers through washing, a copolymer of a (meth)acrylate ester having a fluoroalkyl group (hereinafter also referred to as a fluorine-containing compound) and a hydrophilic group-containing compound is known (see JP-A-53-134786, JP-A-59-204900 and JP-A-62-7782).
However, fiber woven fabrics and the like treated with these fluorine-containing copolymers do not always have satisfactory washing durability and also have a tendency not to have sufficient and satisfactory soil releasability against persistent soils (for example, waste oil such as used engine oil).
It is considered that oil repellency and flip-flop properties are important so as to obtain sufficient soil releasability and, in air, perfluoroalkyl groups (hereinafter abbreviated to Rf groups) are oriented on the surface and high oil repellency is exhibited. In contrast, in water, Rf groups retract and hydrophilic groups are oriented on the surface, and thus soils are easily removed. Flip-flop properties are properties in which a surface molecular structure varies depending on the environment in air and water, and are proposed by Sherman et al. [P. Sherman, S. Smith, B, Johannessen, Textile Research Journal, 39, 499 (1969)]
When the Rf group has a short chain length, oil repellency tends to deteriorate as crystallinity of Rf decreases and an article to be treated is easily contaminated with oil soils. Therefore, a stain-proofing agent having Rf group containing substantially 6 or more carbon atoms has been used (see JP-A-53-134786 and JP-A-2000-290640).
Further, recently, with respect to a compound containing the Rf group having 8 carbon atoms obtained by telomerization, Federal Register (FR Vol. 68, No. 73/Apr. 16, 2003 [FRL-2303-8]; EPA Environmental News FOR RELEASE: MONDAY APR. 14, 2003 EPA INTENSIFIES SCIENTIFIC INVESTIGATION OF A CHEMICAL PROCESSING AID;
and
EPA OPPT FACT SHEET Apr. 14, 2003
have announced that a “telomer” may possibly metabolize or decompose to perfluorooctanoic acid (hereinafter referred to as “PFOA”).
EPA (Environmental Protection Agency of USA) has announced that the EPA intensifies the scientific investigation on PFOA (cf. EPA Report “PRELIMINARY RISK ASSESSMENT OF THE DEVELOPMENTAL TOXICITY ASSOCIATED WITH EXPOSURE TO PERFLUOROOCTANOIC ACID AND ITS SALTS”).